A national harmonised data collection network for neurodevelopmental disorders: A transdiagnostic assessment protocol for neurodevelopment, mental health, functioning and well‐being

Abstract Background Children with neurodevelopmental disorders share common phenotypes, support needs and comorbidities. Such overlap suggests the value of transdiagnostic assessment pathways that contribute to knowledge about research and clinical needs of these children and their families. Despite this, large transdiagnostic data collection networks for neurodevelopmental disorders are not well developed. This paper describes the development of a nationally supported transdiagnostic clinical and research assessment protocol across Australia. The vision is to establish a harmonised network for data collection and collaboration that promotes transdiagnostic clinical practice and research. Methods Clinicians, researchers and community groups across Australia were consulted using surveys and national summits to identify assessment instruments and unmet needs. A national research committee was formed and, using a consensus approach, selected assessment instruments according to pre‐determined criteria to form a harmonised transdiagnostic assessment protocol. Results Identified assessment instruments were clustered into domains of transdiagnostic assessment needs, which included child functioning/quality of life, child mental health, caregiver mental health, and family background information. From this, the research committee identified a core set of nine measures and an extended set of 14 measures that capture these domains with potential for further modifications as recommended by clinicians, researchers and community members. Conclusion The protocol proposed here was established through a strong partnership between clinicians, researchers and the community. It will enable (i) consensus driven transdiagnostic clinical assessments for children with neurodevelopmental disorders, and (ii) research studies that will inform large transdiagnostic datasets across neurodevelopmental disorders and that can be used to inform research and policy beyond narrow diagnostic groups. The long‐term vision is to use this framework to facilitate collaboration across clinics to enable large‐scale data collection and research. Ultimately, the transdiagnostic assessment data can be used to inform practice and improve the lives of children with neurodevelopmental disorders and their families.


INTRODUCTION
It is estimated that one in 10 children meet diagnostic criteria for at least one neurodevelopmental disorder (Arabiat et al., 2018;McGuire et al., 2019). These disorders are often lifelong and impact cognitive, social and emotional development from the first years of life onwards (American Psychiatric Association, 2013). The most frequent referrals for neurodevelopmental assessment include global developmental delay, autism spectrum disorder (autism), attention-deficit hyperactivity disorder (ADHD) and specific learning difficulties (e.g., dyslexia), but may also include cerebral palsy, Tourette's syndrome, single gene disorders (e.g., Fragile X Syndrome), and language disorders (Boyle et al., 2011;Hiscock et al., 2011;Kayrouz et al., 2014;Lo et al., 2017).
It is well established that children with neurodevelopmental disorders who present to health services will commonly receive a single primary diagnosis that guides future treatment (Hiscock et al., 2017;McDowell, 2018). However, diagnostic overshadowing, where symptoms are attributed to an identified condition rather than being considered as indicators of comorbid conditions, is common and occurs irrespective of the complexity with which an individual presents (Hendriksen et al., 2015;Kerns et al., 2015). As a result, clinical practice has been historically narrow in focus and fragmented by professional and diagnostic silos in which clinicians prioritise the needs of a specific neurodevelopmental disorder but fail to address those concerns and difficulties that fall outside their familiarity or expertise. This often means that caregivers will be required to seek treatment for their child in different places to fully meet their needs.
This can lead to increased difficulties accessing and navigating services, unnecessary delays in obtaining supports or a complete absence of a response to these needs (Thapar et al., 2017). These specialist silos can be perpetuated by diagnostic criteria. For instance, until the release of the DSM-5, a child could not be diagnosed with both autism and ADHD despite the high rates of overlap seen both clinically and in research (Gargaro et al., 2011).
A similar diagnosis-specific pattern is present in research, where there are many networks focusing on single neurodevelopmental disorders but far fewer with a transdiagnostic focus. The EU-AIMS (Murphy & Spooren, 2012), SPARK (Feliciano et al., 2018) and Australian Autism Biobank (Alvares et al., 2018) networks in Europe, the United States and Australia, respectively, have established some of the largest networks for the collection of genomic, cognitive and behavioural data to inform diagnosis and clinical interventions for autism. Likewise, the Australian Cerebral Palsy Register has been established to facilitate large-scale data collection to inform on aetiology, outcomes and health service planning in cerebral palsy (Australian Cerebral Palsy Register, 2016). This work has resulted in many impactful research outcomes for children and families. For example, cerebral palsy research networks have substantially improved the detection, intervention, rate and severity of cerebral palsy diagnosis in young children over the last 20 years (King et al., 2020;Novak et al., 2017). Similarly, autism research and clinical networks have substantially advanced our knowledge about early intervention and support for social development, as well as current intervention patterns for autistic children and adolescents (Hazlett et al., 2017;Loth et al., 2017;Monz et al., 2019). Although these networks do consider comorbidity in their measurements, the fact that they focus on one particular disorder precludes transdiagnostic research into predictors or treatment of symptoms that may be prevalent across disorders.
It is abundantly clear that transdiagnostic assessment and diagnosis pathways are needed in research and clinical practice. Adopting a transdiagnostic approach requires assessment of symptoms, functioning and social factors that may be shared across multiple neurodevelopmental disorders (Finlay-Jones et al., 2019;Thapar et al., 2017). This dimensional approach enables better understanding of needs beyond a single diagnosis and aligns with the National Institute of Mental Health Research Domain Criteria (RDoC) framework (Casey et al., 2014). For example, it is well established that comorbidity in presentation is the rule rather than the exception in neurodevelopmental disorders. Across clinical and population samples, it has been estimated that at least 80% of children with one neurodevelopmental disorder experience multiple, co-occurring neurodevelopmental and psychiatric disorders, as well as far higher rates of other medical comorbidities (e.g., epilepsy, sleep problems and cardiovascular disorders) (Antshel & Russo, 2019;Hiscock et al., 2017;King, 2016;Pahlman et al., 2020;Rommelse et al., 2010).
There is also growing evidence that children with sub-threshold presentations have much higher rates of mental health problems and impairments than the general population, which are associated with negative educational outcomes and poorer functional outcomes in adulthood (Copeland et al., 2015;Zendarski et al., 2020).
Furthermore, there is a high prevalence of mental health problems in caregivers of children with neurodevelopmental disorders (Bromley et al., 2004;Masefield et al., 2020).
Basic science also supports the potential of using transdiagnostic frameworks. Aside from single-gene disorders, neurodevelopmental disorders are largely considered polygenic, sharing common genetic variations that increase risk, and may be related to symptoms and levels of functioning (Niemi et al., 2018;Sengupta et al., 2018). Similarly, environmental variables linked to neurodevelopmental risk, such as prematurity, low birth weight, increased parental age, compromised prenatal environment and lower socioeconomic status have been associated with multiple neurodevelopmental disorders (Carlsson et al., 2020;Han et al., 2021;Sciberras et al., 2017).

Development of a harmonised, transdiagnostic data collection network for neurodevelopmental disorders
There is an emerging consensus that research would benefit more through harmonisation and consolidation of data across neurodevelopmental disorders (Casey et al., 2014;Thapar et al., 2017).
Likewise, the importance of harmonised data collection as part of standard clinical practice is beginning to be acknowledged (Krause

Key points
What's known?
� Children with neurodevelopmental disorders and their families share many common needs. National and international harmonised data collection networks across neurodevelopmental disorders are not well-developed.

What's new?
� We present a consensus driven transdiagnostic assessment protocol with researchers, clinicians and community groups and across many specialist clinics.

What's relevant?
� This protocol is proposed to be used nationally and internationally to establish one of the first large scale transdiagnostic databases.  , 2021). There is growing recognition that children with neurodevelopmental disorders share common needs that have significant impacts on individual and family functioning and developmental outcomes. The importance of this in policy has been recently highlighted by funding bodies. For example, Australia's National Disability Insurance Agency (NDIA) criteria for funding has moved towards a diagnostically agnostic model, with a diagnosis-neutral suite of assessment tools to identify support needs (NDIA, 2020). This diagnosis-agnostic approach aligns with the International Classification of Functioning, Disability and Health (ICF) framework which also supports universally accepted frameworks to describe functioning across different conditions and groups (WHO, 2001).
Despite this growing awareness, internationally, we are not aware of any agreed data collection protocols and/or platforms that are integrated with clinical services and facilitate the collection of standardised, transdiagnostic information from the broad group of children with neurodevelopmental disorders and their families. Such a platform would have the potential to facilitate stronger and more coherent links between research and clinical services for children with neurodevelopmental disorders. Identification of transdiagnostic needs will provide clinicians with knowledge of concerns and needs that extend beyond the primary diagnoses. Identification of these needs will provide clinically actionable options that may enable a more integrative approach to care and improve patient outcomes.
Recent findings indicate that there is strong enthusiasm and a preference for standardised electronic data collection amongst families of children with neurodevelopmental disorders . As such, an electronic data collection platform may have a particularly high chance of successful uptake in this cohort. In keeping with the move toward large, unified datasets that can inform both research and clinical practice, such as those used in youth mental health (Lavoie et al., 2020), the aim of this paper was to propose an assessment protocol for harmonised data collection across research centres, hospital-based and community clinics in the field of child neurodevelopment. It was also to establish this protocol in collaboration with a national consortium of researchers, clinicians, and community representatives with extensive experience in the field of child neurodevelopment from across Australia. Using a streamlined protocol would enable researchers to address questions about specific disorders, as well as transdiagnostic questions that reach across disorders. Additional consultation was also sought from the Child Neurodevelopment and Mental Health Team from the University of Sydney. The COS-STAR (Core Outcome Set-Standards for Reporting) guidelines were followed when developing the transdiagnostic assessment protocol (see Table S1).

Engagement with researchers and clinicians
Twenty-six individuals including research academics, psychiatrists, psychologists, paediatric neurologists, neonatologists, paediatricians, epidemiologists, speech pathologists and not-for-profit disability organisation employees took part. They reported on the questionnaires and tools they currently use and those that they felt should be used to harmonise data collection across neurodevelopmental disorders. These individuals came from 23 speciality clinics based at universities or children's hospitals. In total, 14 institutions and hospitals across Australia were represented. 1 Combined, these institutions and hospitals see over 6000 children with neurodevelopmental disorders per year.
Experts were asked to provide information about: (i) the clinical populations they serve (e.g., autism, ADHD); (ii) the estimated proportion of comorbidities seen in presenting patients; (iii) the assessment tools and measures currently being used; (iv) the method by which assessments were being conducted (paper/pencil or electronically); (v) assessment tools and measures that would have transdiagnostic utility across neurodevelopmental clinics/institutes; and (vi) domains that were not currently being measured, but which respondents thought should be measured across neurodevelopmental disorders.

Engagement with the broader neurodevelopmental community
In addition to consulting experts in the field of neurodevelopmental disorders, members of the neurodevelopmental community were consulted, to better understand their concerns and needs and to inform how these needs can be addressed using a transdiagnostic approach. In total, 11 community organisations across Australia were represented 2 . Community members comprised youth and adults with lived experience of a neurodevelopmental disorder, parent advocates, and representatives of these organisations.  Rinehart and Andrew J. O. Whitehouse) was formed to reach a consensus on the domains that should be measured using a transdiagnostic assessment protocol, and the specific assessment tools and measures that would comprise each domain. Research committee members were selected from within Neurodevelopment Australia based on their research and clinical expertise in the field of child neurodevelopmental disorders. The research committee met face-toface, via teleconference, and through email over a period of nine months to reach consensus on domains and specific measures. The technique used to reach consensus was a variant of the Nominal Group Technique. Our approach was similar to that used by Lavoie et al. (2020) when developing a core data set for youth mental health.

Development of harmonised assessment protocol
Research committee members were asked to review the information collected from researchers, clinicians and the broader neurodevelopmental community. Following this, they were asked to answer the following questions: 'What domains should be assessed transdiagnostically in child neurodevelopment', and 'What measures should be used to capture these domains?'. Research committee members were asked to use the information collected and combined this with the wider literature when discussing and making recommendations. All domains and measures were considered by research committee members, with the aim being the creation of an assessment protocol that was appropriate for children aged 0-18 years, irrespective of the specific diagnosis or problems the child was presenting with.
Several criteria were used to select measures for inclusion in the assessment protocol. First, measures needed to be applicable across neurodevelopmental disorders and, where possible, relevant to children and adolescents aged from 0 to 18 years. Second, given the patient-facing time restrictions of many developmental clinics, there was a preference for caregiver-completed measures that were questionnaire-based, with the ability for completion prior to assessment (e.g., via electronic data capture). Third, efforts were made to select measures with sound psychometric properties and where possible, those that have been validated in children and adolescents with neurodevelopmental disorders. Finally, there was a preference for measures that are freely available and in the public domain wherever possible, to ensure ease of access.
To keep the core transdiagnostic assessment protocol as brief as possible, and thereby accessible and attractive to a wider range of hospital and community-based clinics, research committee members were advised to present a protocol that would take no longer than 45 min to complete. Additional domains and measures considered to be transdiagnostically relevant, but that are substantially longer and/ or not accessible in the public domain, were incorporated into an extended transdiagnostic assessment protocol. The rationale for an extended protocol was to allow collection of additional information in clinics with capacity and resources to do so, thereby enabling harmonisation of these measures as well. As the requirements for assessment are quite different from the requirements for monitoring change, a conscious decision was made not to use ability to track change as a selection criterion. A separate outcome set will be developed to measure outcomes and monitor the changing needs of children and families with neurodevelopmental disorders over time.

Feedback from researchers and clinicians -Assessments used in clinics
As shown in Table 1 Abbreviations: ADHD, attention-deficit hyperactivity disorder; Y, Yes. a Early developmental signs -Patients are children who were in the neonatal intensive care unit. Patients are seen routinely until 3.5 years of age. b Developmental assessment -Patients are children who have been referred to an assessment clinic with a suspected developmental delay requiring evaluation. referred for assessment and evaluation due to suspected developmental delay/intellectual disability); eating disorders; autism; ADHD; neuromuscular disorders and epilepsy. The age range of children across the clinics was 0-18 years (see Table S2, for a breakdown of the age range per speciality). Given the high rates of comorbidities across clinical specialties (e.g., experts indicated that approximately 10% of patients presenting to eating disorder clinics present with comorbid autism), a broad range of specialties were included, to capture the diversity of children seen across settings.
Although individual assessments were extensive and varied considerably across specialties (see Table S3, for a full list of measures used), it became apparent that each speciality focussed on similar domains as part of their routine assessment. As displayed in Table 1, a diagnostic interview and/or medical assessment was performed across all specialities, while other domains varied as a function of speciality.
For example, motor functioning was measured in clinics specialising in cerebral palsy, where some degree of motor difficulties are commonly seen in presenting children, whereas cognitive assessments were more often conducted in clinics specialising in global developmental delay, autism and ADHD, where a report of cognitive functioning is typically required for monitoring purposes.
The same group of researchers and clinicians provided feedback on assessment measures and tools they believed would have transdiagnostic utility across all developmental clinics. Each respondent also provided feedback on the domains that were not currently being measured as part of their standard practice, but which they thought should be measured transdiagnostically across clinics. While the individual measures that were recommended varied across specialties (see Table S4, for a full list of measures recommended by each specialty), there was consistency on the domains recommended for transdiagnostic assessment across specialities. As displayed in Table 2, most specialities recommended that information relating to functioning and quality of life should be captured as part of standard clinical practice.
However, fewer than half of these specialities reported that they routinely captured these outcomes, highlighting the gap between the data clinicians believe should be captured, and the data that are currently being captured as part of standard clinical practice.  Table 3.   (Reeve et al., 2013). See Table S5, for this information.

Development of harmonised assessment protocol -Selection of assessment measures
The measures included in the core and extended transdiagnostic assessment protocols are presented in Table 4. For a summary of the psychometric properties of each measure, as well as whether they are freely available for use, please see Table S5. The committee recommended that the core assessment protocol should be administered in full, and the additional measures within the extended assessment protocol administered where possible. Total completion time for the core transdiagnostic protocol is estimated to be between 45 and 60 min, while total completion time for the extended transdiagnostic protocol is expected to be between 100 and 140 min. An advantage of both assessment protocols is that they can be completed by caregivers online before they and their child attend their appointment. This is likely to be particularly important for successful uptake, given our recent findings in developmental clinics where substantially higher response rates were seen for online as opposed to paper completion . Moreover, both the core and extended protocols can be automatically scored before an individual presents at a service, providing clinicians and service providers with a snapshot of individuals, including areas of potential concern, before they arrive for assessment. We provide an overview of each domain in turn.
Child functioning and quality of life Form (Sparrow et al., 2016), is included in the extended transdiagnostic assessment protocol.
T A B L E 3 Community-recommended principles for further development in transdiagnostic research and practice

Principle Description
Adopting a transdiagnostic approach Working in diagnostic and professional silos is not effective. By collaborating and cooperating across disorders, there is potential to learn more about commonalities and differences in disorders, and to have a much larger impact on research and practice There is enormous potential for community organisations to learn from each other and for the strengths of one organisation to benefit other groups and organisations by working together. Certain organisations have particular strengths due to the focus of support for that diagnosis, which can be shared transdiagnostically to benefit the broader community (e.g., Tourette's Australia highlighted strengths of practice in running sibling and community camps; Amaze discussed their post-diagnosis support network) Identifying and attending to individual needs and developing individualised care plans The individual needs of a child beyond their specific diagnosis should be considered. Families should be provided with roadmaps to services and support that are tailored to their child's needs. While a specific diagnosis is helpful for families to understand some of the supports their child will require, addressing individual needs will likely improve outcomes for children and families, as well as their overall interactions with service providers Focus on everyday functioning Services should focus on a child's level of functioning, rather than just the diagnostic label.   (Okyar & Görker, 2020;. A more comprehensive measure of mental health, the Adult Self-Report (ASR; Achenbach & Rescorla, 2003), is recommended in the extended transdiagnostic protocol. In addition to providing an overview of mental health symptom severity, the ASR provides information on adaptive functioning and substance use, as well as an indication of whether the respondent is likely to meet DSM-5 criteria for mental health conditions.

Family background information
A common theme that emerged when considering recommendations from clinics was the need to consistently collect accurate and harmonised background information, such as socio-demographic data, on families presenting to hospital and community-based clinics. Specifically, it was noted that information pertaining to educational attainment and employment of caregivers, as well as family income, is not routinely collected, despite being considered a key domain on which to focus. Additionally, clinicians noted that an understanding of a child's intervention history, as well as caregiver intervention history, is valuable for understanding the interventions that are frequently used, and whether they are similarly used across Appendixes S1 and S2, respectively.

Cognitive functioning (extended transdiagnostic protocol only)
When considering the measures routinely used by neurodevelopmental clinics, it was noted that assessments of cognitive functioning are commonly conducted, however there was no consistency in the assessment or measures used. Cognitive difficulties are commonly associated with poorer outcomes for children and adolescents with neurodevelopmental disorders (Einfeld et al., 2006), and it was noted that an assessment of cognitive functioning is crucial for identifying impairments and recommending appropriate referral pathways (Coghill, 2021). Given that cognitive functioning is typically best assessed using face-to-face measures, and one key aim of the transdiagnostic assessment protocol was to select questionnairebased measures that could be completed by caregivers at home, the decision was made not to include the domain of cognitive functioning in the core transdiagnostic assessment protocol. However, given that executive function has been shown to impact on outcome (Albert et al., 2018;Demetriou et al., 2019), and executive function difficulties are commonly seen across neurodevelopmental disorders (Dajani et al., 2016), a measure of everyday executive function, the Behavior Rating Inventory of Executive Function, Second Edition (BRIEF 2; Gioia et al., 2003Gioia et al., , 2015, is recommended for use in the extended transdiagnostic assessment protocol. Caregivers of children with neurodevelopmental disorders are at increased risk for stress and mental health conditions (Bromley et al., 2004;Masefield et al., 2020;Sawyer et al., 2010;Wesseldijk, Dieleman, van Steensel, Bleijenberg, et al., 2018). As such, it was considered critical that caregiver mental health be measured transdiagnostically. The mental health vulnerabilities common in caregivers have been shown to be associated with broader negative effects for the family, predicting poorer outcomes over time (Wesseldijk, Dieleman, van Steensel, Bleijenberg, et al., 2018). For example, parental stress appears predictive of therapy adherence across neurodevelopmental disorders, such that increased perceived parental stress predicts lower therapy adherence in children diagnosed with autism, ADHD and/or intellectual disability (Loader et al., 2019). Considering caregiver mental health as a transdiagnostic factor may elucidate how caregiver well-being can influence functioning and development in children, irrespective of the specific diagnosis. Assessment of caregiver mental health may also lead to the development of transdiagnostic, evidence-based interventions which could improve outcomes for the whole family.

DISCUSSION
The clinics and research centres surveyed within this paper provide care to a diverse range of families, including a considerable proportion from lower socioeconomic backgrounds. Additionally, the type of interventions accessed by these families are incredibly diverse. Given that families from low socio-economic backgrounds are at increased likelihood of poor outcomes and face increased barriers when attempting to access services (Raouafi et al., 2018;, it was deemed important to collect information on family demographics and socio-economic status. Collection of this information can facilitate the development of pathways to help these families access the services they need. Further, a clearer understanding of the types of interventions used by both children and caregivers was also considered critical, given that interventions are not equally accessed across or within neurodevelopmental disorders (Khetani et al., 2017;Tan-MacNeill et al., 2020;Wright et al., 2015). Collection of these data will likely inform which interventions are most accessible to families, whether certain interventions are more likely to be used by specific groups of individuals, and how we can modify services and increase access to ensure that interventions are accessible to all families who need them, regardless of diagnosis and socioeconomic background.
This transdiagnostic assessment protocol will be promoted and made available to researchers, clinicians and community organisations working in child neurodevelopment research and services across Australia, and potentially internationally, to collect core harmonised transdiagnostic data. These instruments can provide a useful screen for transdiagnostic needs, such as caregiver mental health, child mental health, and functioning supports, that might be needed. On their own, however, they will likely result in false positives and therefore should be used for guiding further clinical investigation and subsequent referral (Chamberlain et al., 2021;Coghill et al., 2021;Goodman et al., 2000;Havdahl et al., 2016). The measures have been selected by researchers and clinicians with expertise in the field, keeping in mind the time and financial constraints of busy hospital-based clinics. Moreover, the measures selected assess key domains of need and concern, as informed by community and clinician engagement. The protocol described in this paper has received ethics approval (2020/ETH02923) and has capacity for national and international collaboration. The transdiagnostic assessment protocol is now being disseminated widely across our network, with members of Neurodevelopment Australia implementing it in their research and clinical services.
The assessment protocol proposed in this paper, and specifically the information collected within it, can be harnessed to provide individualised, needs-based supports and information to families who access services, which may facilitate improved outcomes. For example, caregivers that report significant levels of depression as identified following completion of the protocol could be supported with online resources, psychoeducation and clinical pathways for care. This assessment protocol could therefore facilitate clinical care pathways that may not currently exist in services. Our team is currently working with participating services to co-design streamlined assessments and efficient processes for data collection as well as support pathways and intervention resources that are provided to families and clinicians based on needs identified in the transdiagnostic assessment protocol. In addition, it is already established that these transdiagnostic factors, such as caregiver mental health, may moderate treatment response for children (Campbell et al., 2020;Wesseldijk, Dieleman, van Steensel, Bleijenberg, et al., 2018). The use of a standardised transdiagnostic set may thus be useful for supporting personalised intervention practices for both research and clinical practice.
The proposed harmonised data collection protocol will allow for the development of a large transdiagnostic dataset that can be administered to children with neurodevelopmental disorders and their families who present to hospital-based and community services, as well as research centres around the country. While there are domains relevant across neurodevelopmental disorders that are beyond the scope of the transdiagnostic assessment protocol proposed here (e.g., motor and cognitive assessments, see England-Mason, 2020; Ketelaar et al., 1998;Vaidya et al., 2020;Wilson et al., 2018), the measures in the proposed assessment protocol should add value to current clinical practice and research, as well as having the potential to inform policy making and practice. A summary of the potential value of the assessment protocol across these domains is shown in Table 5. Furthermore, we acknowledge that the measures in the assessment protocol are caregiver-report questionnaires. However, many of these measures have self-report versions available for older children, which will enable us to combine different reports (e.g., self-and caregiver-report) as needed.
Based on the data access and sharing policies that our group are currently preparing, and with ethics and governance approval across sites, individuals and groups who contribute data using the assessment protocol will have access to the data, and also to the expertise of the researchers and clinicians who have developed the protocol. This approach will facilitate data sharing and linkage, and future collaborative research opportunities. Given the difficulties in constructing a core set of measures that have been outlined when discussing the benefits and challenges of this type of integrative data analysis (Hussong et al., 2013), a major benefit of the proposed assessment protocol is that it comprises an agreed upon set of measures that will be consistently used by research centres and clinics nationally. Interested collaborators, including researchers and clinicians, are invited to contact the authors to discuss implementation of the protocol in their setting and can contribute to the dataset by using the transdiagnostic assessment protocol with their cohorts.
This will promote a collaborative approach to data analysis, and will enable substantially increased statistical power, the potential to address research questions that cannot be answered by a single research centre or clinic, and importantly, the opportunity to develop a collective science of transdiagnostic assessment, where similarities and differences across clinical cohorts are evaluated. Data will be collected, stored and shared electronically on secure, Universitymanaged servers. Moreover, while the measures within the transdiagnostic assessment protocol were not selected based on their ability to track change or measure outcomes over time, our vision is to develop a complementary protocol designed to measure needs and outcomes, and monitor change over time. Participating children and families will be invited to complete this separate protocol, enabling us to conduct follow-up assessments to gain insight into outcomes and change over time.
A long-term goal of this transdiagnostic assessment protocol is to enable the development of investigator-led, multi-site, transdiagnostic research studies which can address the needs of many children and families, as opposed to single-site, diagnosis-specific studies, which are restricted to addressing the needs of a single population. Based on the services with which we are currently engaged, there is the potential for this assessment protocol to be administered to thousands of children per year, a sample which will increase as more research and clinical services utilise the protocol.
Further, the research questions that could be addressed using data collected in this assessment protocol are numerous, with enormous potential for future research collaborations across universities and T A B L E 5 Potential value of transdiagnostic assessment protocol across multiple domains

Domain Potential value of assessment protocol
Clinical services Provides structure to assessment and recording of information at the time of first presentation. Highlights and clarifies complexity in cases, and provides a clear baseline from which change can be measured. Enables clinical services to measure symptoms and areas of need, rather than focussing solely on an individual diagnosis. Allows clinicians to provide referrals and information resources based on transdiagnostic needs identified

Research
Facilitates national data collection in the neurodevelopment space and allows large-scale research questions to be addressed. Provides opportunity to understand the suitability of these measures for culturally and linguistically diverse groups Enables data linkage on a national scale following participant consent. Data can be linked with other routinely collected data, including hospital admissions, NDIA service utilisations, the Medicare and pharmaceutical Benefits Schemes, the Juvenile Justice Minimum data Set, the National Assessment program for Literacy and Numeracy, and census data Policy and Practice National implementation of the assessment protocol would enable identification of the cross-cutting needs of children with neurodevelopmental disorders and their families. This information could be used by policy makers to inform on national resource allocation and funding decisions. This transdiagnostic approach has potential to lead to positive downstream approaches to better support children at school, where a positive or negative experience can make an enormous contribution to mental health outcomes they will be at far greater risk of delay in other domains (such as social and cognitive) and this interaction requires a more integrative framework to comprehensively address needs.
While the potential value and benefit of a harmonised transdiagnostic assessment protocol is clear and there is evidence that the families accessing these services would prefer to provide information online as opposed to on paper , we acknowledge that there are potential barriers to successful implementation. For instance, additional resources and support are required to ensure an assessment protocol of this sort is useful to all involved. While support and engagement from peak bodies and stakeholders is critical, adequate infrastructure is key to ensuring the successful implementation of a national transdiagnostic assessment protocol as proposed in this paper. An economic evaluation will be conducted from both a health system and societal perspective. This is essential to determine whether the costs to the service that are associated with implementation (e.g., infrastructure, resources) are feasible across clinics and if the benefits of the protocol (e.g., identification of transdiagnostic needs and subsequent referral to appropriate services) outweigh these implementation costs. Similarly, for successful implementation of this assessment protocol, it is important that state health departments support its implementation and help to facilitate the rollout across services where required. To enable ongoing evaluation of the transdiagnostic assessment protocol, we will use an implementation framework, assessing key implementation outcomes of acceptability, appropriateness, feasibility, adoption, costs, fidelity and sustainability (Proctor et al., 2011). This will allow for the essential evaluation of cost, successful implementation to new sites and national scalability.
Another potential barrier to implementation of this protocol lies in the cost of purchasing the assessment measures. In line with our aim to select measures in the public domain to ensure ease of access, the majority of measures selected for inclusion in the core assessment protocol are freely available and selected based on their ability to identify transdiagnostic needs. However, the measures included in the extended assessment protocol have varying degrees of licensing costs and registration requirements associated with their use. These measures were selected given their strong psychometric properties and ability to comprehensively assess the domains of interest.
However, participating clinics must take these factors into consideration when deciding whether they have the resources to administer the extended assessment protocol.
The measures in this assessment protocol were selected by experts in the field following multiple consultations and using a transdiagnostic approach. Nevertheless, we note that the approach used to develop the transdiagnostic assessment protocol is not without its limitations. While the COS-STAR guidelines were followed when developing this protocol, a more structured method of eliciting and synthesising stakeholder feedback may have enabled greater replicability by other groups. Further, despite the expertise of the research committee, we note that there was no external validation of the recommended assessment protocol through a large-scale Delphi survey. In spite of these limitations, the transdiagnostic assessment protocol proposed here still has immense potential to harmonise data collection, which is often fragmented across services and conditions, and to provide much-needed insight into the needs of children with neurodevelopmental disorders and their families.
In summary, while the science and application of transdiagnostic research and practice is in its infancy, this paper proposes a harmonised transdiagnostic assessment protocol which can be used by researchers, clinicians and community organisations to understand better the needs, concerns and vulnerabilities of children with neurodevelopmental disorders and their families. By engaging researchers, clinicians and community members across the field of neurodevelopmental disorders, a transdiagnostic assessment protocol has been developed, that has the potential to address the needs of children and families in the neurodevelopment space. This approach is the first step in facilitating nationwide research that is both directly informed by the community and is clinically relevant for families accessing hospital-and community-based developmental services. The long-term vision of this approach is to conduct research which will ultimately improve the lives of children with neurodevelopmental disorders and their families.